Overview & Objective(s): Everglades restoration planning requires an understanding the impact of natural and human-induced environmental change on wetland stability. This project initially focused on tree-island development and trends and has expanded into two other systems: the sawgrass ridge and slough system and marl prairies. For each system, restoration targets are being proposed, even though little data exists on their predrainage extent and ecosystem dynamics. Initial goals of the project included: determine geologic and hydrologic controls on tree-island formation, development and sustainability; establish vegetational trends in tree-island development; determine the role of tree islands in the geochemical budget of nutrients; and investigate the use of sediment phosphorus as a tracer of historic bird populations in the Everglades.

Investigations of the Ridge and Slough system are directed to: determine the longevity of the features; document changes in spatial extent of sawgrass ridges and sloughs; determine past rates of peat accretion in ridges vs. sloughs; determine whether sawgrass ridges are analogs for sites of tree-island formation; and assess the response of ridges and sloughs to natural and anthropogenic hydrologic changes. Investigations of marl prairies are designed to determine whether the distribution and vegetational composition of marl prairies has changed over the last century.

Status: By the end of FY05, cores will have been collected on 39 tree islands in Loxahatchee NWR, WCA 2A, 3A, 3B, and Everglades National Park (Shark River Slough and Taylor Slough). Pollen and geochronologic data have been generated from 27 cores representing 15 tree islands. Six transects of cores were collected across "pristine" and altered sawgrass ridges and sloughs sites in WCA 3A. From these, pollen analysis is complete on surface samples and four transects, representing a total of 11 cores. In FY 04-05, field work included coring of strand and pop-up tree islands in Loxahatchee NWR and tree islands in the East Everglades Expansion Area of Everglades National Park. A long core (5 meters) also was collected in Deep Lake (BCP) to evaluate natural and anthropogenic patterns of change in an ancient sink-hole lake in a relatively pristine area of the Preserve. Analysis of sediment cores collected in marl prairies in the western Everglades as a pilot study indicated that pollen, plant macrofossil, and ostracode records all provide good records of vegetational and hydrologic change in marl-accumulating systems, and we intend to sample other such sites to document the timing of vegetational changes and correlate them with specific hydrologic events. In Loxahatchee, we collected cores on nine tree islands and nine marshes in the northern, central, and southern reaches of the Refuge to establish the original ecosystem structure and composition and evaluate changes in response to 20th century management changes. During the summer of FY05, four tree islands in the East Everglades Expansion Area of Everglades National Park will be cored in collaboration with archeological research conducted by park personnel.

Bernhardt, C.E. and Willard, D.A., 2004. Development and Stability of the Everglades Ridge and Slough Landscape: Records from three transects in Water Conservation Area 3A. U.S. Geological Survey Open-file Report 2004-1448.

This study supports several of the projects listed in the DOI science plan (specifically: Arthur R. Marshall Loxahatchee NWR Internal Canal Structures; Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement; and Combined Structural and Operational Plan) by (a) documenting the timing of tree-island formation across the region; (b) establishes patterns of vegetation development and geochemical changes on the islands; (c) comparing development of different types of tree islands; (d) developing a model of tree-island formation that may be used in restoration of degraded islands and, possibly, creation of new islands; and (e) determining the duration of flooding or drought that tree islands can tolerate before changes in aerial extent occur.

This study supports the Combined Structural and Operational Plan project (CSOP and Mod Waters; p. 70) as it (1) generates information that will improve ecological models and make them more suitable for application of the Natural Systems Model (p. 71).

Key Findings:

Tree islands throughout the greater Everglades ecosystem were affected by 20th century hydrologic change, but impacts on plant community composition and tree-island size vary throughout the region.

The basic Ridge and Slough structure of WCA 3A has existed for at least 1,000 years; the position of the ridge-slough transition zone has fluctuated in response to recent changes in hydrology.

Pollen, seed, and ostracode assemblages from cores collected in marl prairies indicate a shift to drier conditions in the early 20th century; pending geochronological analyses will clarify the timing of the change.